This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-249727, filed Aug. 21, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a magnetic recording medium used in a peripheral memory device of an electronic computer and used for the recording of image informations and acoustic informations, particularly, to a perpendicular magnetic recording medium for the perpendicular recording system.
With improvement in the performance of an electronic computer, with propagation of the digital system in the image and acoustic data, and with improvement in the information of image, which have been achieved in recent years, a magnetic recording medium for higher recording density has come to be required in various applications such as, particularly, the peripheral recording apparatus of an electronic computer (HDD) and an image data acoustic data recording apparatus (DVTR).
If it is intended to achieve a high density recording by making smaller the recording bit in, for example, the ordinary longitudinal recording, a problem is generated that the coercive force is rendered higher for suppress the thermal decay of the recording bit with the result that the writing by the head became difficult. In order to avoid this problem, proposed in recent years is a perpendicular magnetic recording medium using a perpendicularly magnetized film having a perpendicular anisotropy.
The perpendicular magnetic recording medium used in a perpendicular magnetic recording system comprises in general a soft magnetic underlying film and a perpendicularly magnetized film formed on the underlying film. It is desirable for the soft magnetic underlying film to have a high permeability and a high saturation magnetic flux density. In this medium, however, a domain wall in soft magnetic underlying film is generated, giving rise to an unstability of the recording magnetization such as erasing and demagnetization of the recording data derived from the domain wall migration caused by the external floating magnetic field.
A measure against the domain wall is proposed in, for example, Japanese Patent Disclosure (Kokai) No. 11-149628. It is proposed that a granular structure using fine particles of a hard magnetic material is employed in the soft magnetic underlying film so as to obtain a magnetic recording medium that does not generate a domain wall. However, the soft magnetic underlying film of the particular structure exhibits soft magnetic properties under room temperature and, thus, has a residual magnetization, leading to an inconvenience that a medium noise is generated under the influence of the residual magnetization.
A first object of the present invention, which has been achieved in view of the situation described above, is to provide a perpendicular magnetic recording medium having a low noise and capable of a high density recording.
A second object of the present invention is to provide a perpendicular magnetic recording apparatus having a low noise and capable of a high density recording.
According to one aspect of the present invention, there is provided a perpendicular magnetic recording medium, comprising a nonmagnetic substrate, an underlying film formed on the nonmagnetic substrate, and a perpendicular magnetic layer formed on the underlying film, the underlying film consisting of a layer exhibiting super paramagnetism.
According to another aspect of the present invention, there is provided a perpendicular magnetic recording-reproducing apparatus, comprising a perpendicular magnetic recording medium, driving means for supporting and rotating the perpendicular magnetic recording medium, a magnetic head including an element for recording information in the perpendicular magnetic recording medium and an element for reproducing the recorded information, and a carriage assembly supporting the magnetic head such that the magnetic head is movable relative to the perpendicular magnetic recording medium, wherein the perpendicular magnetic recording medium comprises a nonmagnetic substrate, an underlying film formed on the nonmagnetic substrate and consisting of a layer exhibiting super paramagnetism, and a perpendicular magnetic layer formed on the underlying film.
According to the present invention, it is possible to provide a magnetic recording medium capable of suppressing the noise caused by the residual magnetization and domain wall under room temperature of the underlying film and also capable of achieving a high density recording with a low noise.
The present invention also provides a magnetic recording apparatus capable of suppressing the noise caused by the residual magnetization and domain wall under room temperature of the underlying film and also capable of achieving a high density recording with a low noise.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.